Winder wonderland in Hyde Park was pretty fun. Can’t entirely comment on the rides , but the food, games and drinks all make for a great night out. Speaking to one of the guys working at the funfair (Jimmy!) , was quite interesting. Apparently it took at day and a half to install the Ferris wheel and the quietest times to go would be on a Tuesday evening, you’d probably have the place to yourselves.
I’d recommend taking a casual walk out from Marble Arch if crowds scare you.